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Abstract The Prairie Pothole Region (PPR) of North America contains millions of small depressional wetlands with some of the highest methane (CH₄) fluxes ever reported in terrestrial ecosystems. In saturated soils, two conventional paradigms are (a) methanogenesis is the final step in the redox ladder, occurring only after more thermodynamically favorable electron acceptors (e.g., sulfate) are reduced, and (b) CH₄is primarily produced by acetoclastic and hydrogenotrophic pathways. However, previous work in PPR wetlands observed co‐occurrence of sulfate‐reduction and methanogenesis and the presence of diverse methanogenic substrates (i.e., methanol, DMS). This study investigated how methylotrophic methanogenesis—in addition to acetoclastic and hydrogenotrophic methanogenesis—significantly contributes to CH₄flux in surface sediments and thus allows for the co‐occurrence of competing redox processes in PPR sediments. We addressed this aim through field studies in two distinct high CH₄emitting wetlands in the PPR complex, which coupled microbial community compositional and functional inferences with depth‐resolved electrochemistry measurements in surficial wetland sediments. This study revealed methylotrophic methanogens as the dominant group of methanogens in the presence of abundant organic sulfate esters, which are likely used for sulfate reduction. Resulting high sulfide concentrations likely caused sulfide toxicity in hydrogenotrophic and acetoclastic methanogens. Additionally, the use of non‐competitive substrates by many methylotrophic methanogens allows these metabolisms to bypass thermodynamic constraints and can explain co‐existence patterns of sulfate‐reduction and methanogenesis. This study demonstrates that the current models of methanogenesis in wetland ecosystems insufficiently represent carbon cycling in some of the highest CH₄emitting environments. 

Abstract Wetlands are a major source of methane emissions and contribute to the observed increase in atmospheric methane over the last 20 years. Methane production in wetlands is the final step of carbon decomposition performed by anaerobic archaea. Although hydrogen/carbon dioxide and acetate are the substrates most often attributed to methanogenesis, other substrates—such as methylated compounds—may additionally play important roles in driving methane production in wetland systems. Here we conducted mesocosm experiments combined with genome-resolved metatranscriptomics to investigate the impact of diverse methanogenic substrate amendment on methanogenesis in two high methane-emitting wetlands with distinct geochemistry, termed P7 and P8. Methanol amendment resulted in high methane production at both sites, whereas acetate and formate amendment only stimulated methanogenesis in P7 mesocosms, where aqueous sulfide concentrations were lower. In P7 sediments, formate amendment fueled acetogenic microbes that produced acetate, which was subsequently utilized by acetoclastic methanogens. In contrast to expression profiles in P7 mesocosms, active methylotrophic methanogen genomes from P8 showed increased expression of genes related to membrane remodeling and DNA damage repair, indicative of stress tolerance mechanisms to counter sulfide toxicity. Methylotrophic methanogenesis generates higher free energy yields than acetoclastic methanogenesis, which likely enables allocation of more energy toward stress responses. These findings contribute to the growing body of literature highlighting methylotrophic methanogenesis as an important methane production pathway in wetlands. By using less competitive substrates like methanol that provide greater energy yields, methylotrophic methanogens may invest in physiological strategies that provide competitive advantages across a range of environmental stresses. 

Abstract Many challenges remain before we can fully understand the multifaceted role that natural organic matter (NOM) plays in soil and aquatic systems. These challenges remain despite the considerable progress that has been made in understanding NOM’s properties and reactivity using the latest analytical techniques. For nearly 4 decades, the International Humic Substances Society (IHSS, which is a non-profit scientific society) has distributed standard substances that adhere to strict isolation protocols and reference materials that are collected in bulk and originate from clearly defined sites. These NOM standard and reference samples offer relatively uniform materials for designing experiments and developing new analytical methods. The protocols for isolating NOM, and humic and fulvic acid fractions of NOM utilize well-established preparative scale column chromatography and reverse osmosis methods. These standard and reference NOM samples are used by the international scientific community to study NOM across a range of disciplines from engineered to natural systems, thereby seeding the transfer of knowledge across research fields. Recently, powerful new analytical techniques used to characterize NOM have revealed complexities in its composition that transcend the “microbial” vs. “terrestrial” precursor paradigm. To continue to advance NOM research in the Anthropocene epoch, a workshop was convened to identify potential new sites for NOM samples that would encompass a range of sources and precursor materials and would be relevant for studying NOM’s role in mediating environmental and biogeochemical processes. We anticipate that expanding the portfolio of IHSS reference and standard NOM samples available to the research community will enable this diverse group of scientists and engineers to better understand the role that NOM plays globally under the influence of anthropogenic mediated changes.